Shaft kiln for the burning of cement, lime, dolomite and similar substances, and method of operating said kiln



Nov. 25, 1958 H R SUTER 2,861,788

SHAFT KILN FOR THE BURNING OF CEMENT, LIME, DOLOMITE AND SIMILAR SUBSTANCES, AND METHOD OF OPERATING SAID KILN Filed Jan. 28, 1955 IN VEN TOR.

ilnited States Patent F SHAFT KILN FOR THE BURNING 0F CEMENT, LIME, DOLOMITE AND SIMILAR SUBSTANCES, AND METHOD OF OPERATING SAID KILN Hans Rudolf Su fer, Zurich, Switzerland, assignor to L. von Roll AG., Zurich, Switzerland, a Swiss com- Application January 28, 1955, Serial No. 484,778

Claims priority, application Switzerland January 29, 1954 9 Claims. (Cl. 263-30) The present invention relatesto the operation of shaft kilns for burning cement, lime, dolomite and similar substances. The operation may be carried out in particular in connection with the burning of cement raw meal in a high-capacity shaft kiln.

In view of the sensitivity of raw meal to overheating, on the one hand, and of the minimum temperature required for complete sintering with in a reasonable time, on the other hand, good results have been achieved with shaft kilns used for small quantity production as such shaft kilns are operated similar to conventional rotary kilns. However, it has so far not been possible to build shaft kiln units for large outputs because with shaft kilns of relatively large diameter the distribution of air over the useful or effective cross-section has not yet proved satisfactory and constant supervision of the kiln in operation is necessary to achieve uniform burning of the clinker at all points of the shaft cross-section.

Since experience has shown that these difficulties can still be overcome with shaft kilns of fairly small diameter, e. g. 1.5 m. to 1.8 m., but increase considerably if the diameter is between 2.0 m. and 2.4 m., it has already been suggested to equip shaft kilns of fairly large diameter with a core member arranged approximately concentrically within the interior of the shaft. In this way the useful cross-section of the shaft can be increased without the distance between the closest walls bounding the shaft cross-section being widened beyond a desired extent. In the operation of such shaft kilns equipped with cores, however, difliculties of thermal origin have always arisen hitherto in connection with the outer Walls of the .core and these difliculties have prevented this design of shaft kiln from being introduced on a large scale.

The present inventionaims at eliminating these drawbacks andrelates to the operation of a-shaft kiln for burning cement, lime, dolomite and similar substances, in which shaft kiln an approximately concentrically arranged core extend-s at least along a part of the kiln shaft. The invention is characterized by the fact that the outer wall or walls of the core, which bound the useful kiln shaft space and extend radially inwards, are cooled by a coolant at least along certain zones of the kiln shaft so as to influence the burning process in the kiln shaft space.

The shaft kiln according to the invention is characterized by the fact that the core arranged approximately concentrically in the shaft kiln and extending at least along a part of the kiln shaft, can be cooled at least at certain sections of its outer walls. Typical embodiments of the invention will now be described in detail in conjunction with Figs. 1 to 6 of the attached drawing in which:

Fig. 1 is a diagrammatic elevational view of a shaft kiln according to the invention, drawn partly in longitudinal section;

Figs. 2 to 4 are diagrammatic horizontal cross-section of various typical embodiments of the kiln shaft according to the invention;

Figs. 5 and 6 are an elevational yiew in longitudinal 2,861,788 Patented Nov. 25, 1958 2 section and a horizontal plan view, respectively, of a further embodiment of the kiln shaft according to the invention.

Fig. 1 shows a shaft kiln of conventional type having the shaft 1, which is cylindrical in shape and is provided with a structure embodying the invention. By means of a suitable charging device 2 the material to be processed normally a mix of combustion material and fuel, pressed into nodules or 'briquettesis conveyed to the kiln shaft and fills up the latters useful cross-section .to just beneath the charging device 2. In the topmost zone of the shaft the material to be processed is mostly predried by hot waste gases which are passed through this zone. The whole charge moves down .through the kiln shaft 1 at a speed determined by the discharging device'3 and, after passing through the'predrying zone, reaches the actual sintering zone. Here, the fuel admixed to the material to be processed 'is burnt up, the combustion air necessary therefor being supplied through a pipe 4 at the bottom end of the shaft and serving at the same time to cool the lower zones of the sintered charge.

It is, however, well known that in a kiln shaft Without a core, particularly if the crosssecti-on of the shaft is circular, the quantity of air flowing through the charge is noticeably smaller in the "neighbourhood of the axis than in the regionlof the walls; this is caused by the loosening action exerted by'the walls on the structure of the charge moving down the kiln. By way of example, cement raw meal can still be processed with perfect results in shaft kilns with an internal shaft diameter of to cm., but as soon as the internal shaft diameter exceeds about 200 cm., the results are no longer satisfactory. This shows, therefore, that, in respect of the pertinent composition of the material and the prevailing conditions, the maximum permissible distance between the closest walls of the kiln shaftidentical with the internal diameter in the case of a circular shaft-is about 180 cm. Such a value for the maximum permissible vertical distance between the closest shaft walls can be ascer tained for any composition of material and for the most diverse working parameters.

In order to give the kiln shaft a large useful crosssection despite the specified maximum permissible vertical distance between the closest walls, a core 5 is incorporated in the shaft kiln as shown in Fig. 1. The said core will preferably be approximately concentric to the kiln shaft and have .a circular cross-section, the distance between the outer Wall 6 of'the core and the inner wall 7 of the shaft being .everywhere the same. In the typical embodiment illustrated in Fig. 1 the core 5 only extends along a part of the whole kiln shaft 1, at least, however, along the sintering zone orsection and the first part of the cooling zone or section directly beneath, and consists of a cylindrical metal hollow body. This metal hollow body is reduced in diameter along the sintering zone, for instance, and is lequipped'with a fireproof covering 8 against the lowermost end thereof abut duct or pipe means 9, 10 as shown. The metal hollow body is provided with double outer walls, in the tubular interspace 9 of which there flows a coolant, for instance water or cooling air. The coolant is passed via the aforesaid pipe or tube 10 through the interior of the core, rises up along the outer wall in the interspace or tubular space 9, thus cooling both the said wall and the fireproof covering 8, and leaves the core 5 via the pipe 11. Owing to the covering 8 of the metal hollow body and the controlled cooling of the outer walls of the core, specified thermal conditions can be created to prevail particularly in the sintering zone both at the inner and outer Walls bounding the kilns useful space. In this way, however, the advantage, intended by the incorporation of a core, of a s ec fied v tica i tance be w e t los wa l bounding the useful cross-section becomes really utilizable for the first time. Without this possibility of cooling envisaged by the invention the thermal conditions between the inner and outer walls are naturally always very different, are dependent at the inner Wall on structural requirements and are virtually uncontrollable. On the other hand, the present invention now enables a shaft kiln equipped with a core to be operated under optimum conditions, it being possible to influence as desired the thermal conditions at the inner wallwhich do not. necessarily have to be identical with those at the outer wall so that a substantially uniform temperature at any horizontal cross-section of the shaft kiln is obtained.

The shaft kiln for applying the operation according to the invention is of course in no way limited to the structural embodiment shown in Fig. 1, but can be designed in a wide variety of ways, some examples of which are reproduced diagrammatically in Figs. 2 to 6.

Fig. 2 shows an embodiment of a circular kiln shaft with an outer wall 12 and a concentrically arranged inner wall 13 forming a hollow core and giving a circular useful cross-section 14 which receives the column of material when the kiln is in operation. Cooling is here effected, by way of example, by means of longitudinal ducts 15 in the inner wall, in which ducts the coolant flows from the top downwards and then back to the top again inside the core. With this design of shaft kiln the useful crosssection may also be very large without the vertical distance between the closest bounding walls being altered.

The wall of the core can of course also be cooled in other suitable ways, for instance by the use of profiled bricks having longitudinal grooves open to the inside. Similarly, the core does not in any way need to be hollow.

A further typical embodiment of the shaft kiln is shown in Fig. 3 in which the kiln cross-section is oval and an oval core 16 is provided. The useful cross-section 17 is an oval ring which is everywhere equidistant from the wall. With this embodiment it is advantageous to choose a shape of cross-section of which the boundary lines form so-called compound curves consisting of circular arcs with not more than two diflerent radii. Such a configuration of the shaft cross-section enables the latter to be made with shaped bricks 18a or 18b having only two different radii of curvature. Here by way of example the core is strongly built and has longitudinal ducts 19 for the coolant. This type of core is particularly suitable for operation with an adjustable air stream as coolant. A core can of course also be provided with a hollow space or with liquid cooling.

A further embodiment of the shaft kiln is illustrated in Fig. 4. Here the annular useful cross-section consists of partly straight, partly curved bounded surface elements, for instance of the two semi-circular surfaces 20 and the two rectangular surfaces 21 located between them. The concentrically arranged core 22 is equipped with longitudinal ducts 23 for a gaseous or liquid coolant. If the core is of adequate width, it can also be designed as a hollow body.

The typical embodiments of the kiln shaft according to the invention described hitherto relate to forms of the said shaft in which there is always a connected useful cross-section. The present invention, however, is not confined to this, but can also be realized by subdividing the entire useful cross-section of the kiln shaft into several separate cross-section surfaces by means of suitably arranged and cooled dividing walls, in which case a predetermined maximum value for the vertical distance between the closest walls must not be exceeded for these separate surfaces.

A typical embodiment of such a kiln shaft with a subdivision into three separate useful cross-sections of equal size is shown in the form of an elevational section view in Fig. and a horizontal top plan view in Fig. 6. In the top part of the kiln shaft, which is, by way of example, circular in shape, three radially arranged. dividing walls 25, 26 and 27 are provided which start from the outer wall 24 of the kiln shaft and converge along the axis of the shaft. Between the dividing walls 25, 26, 27, each of which is staggered at an angle of in respect of the other, and the outer wall 24 three separate shaft sections 28, 29 and 30 with sector-shaped useful cross-sectional areas are produced. By choosing appropriate thicknesses for the dividing walls and shaping core part 31, which extends along the shaft axis, accordingly, the maximum permissible vertical distance between the closest walls of the separate shaft sections 28, 29, 30 can be ensured whatever the diameter of the circular shaft. The core part 31, extending along the shaft axis and common to the dividing walls 25, 26, 27, has an adequately large cross-section and is provided with a longitudinal duct 32, whilst the dividing Walls 25, 26, 27 each have a shallow duct 33 and 35 respectively for the coolant.

The number of radially arranged and cooled dividing walls thus provided depends entirely, of course, on the dimensions of the kiln shaft. If the diameter is fairly small, one central dividing wall extending through the shaft axis can be used for example and the kiln shaft divided into only two sections of equal size. On the other hand, however, it is also possible to use a plurality of radially arranged cooled dividing walls with a common hollow core. Similarly, such radially arranged, cooled dividing walls can also be used with shaft configurations which have, besides, a cooled core, the useful cross-section of which is therefore of annular configuration, as shown by way of example in Fig. 2.

From Fig. 5 it can be seen that with this typical embodiment of the kiln shaft according to the invention, the subdivision of the interior of the shaft into three longitudinal sections is only effected in the upper part of the said shaft and the three dividing walls end at the points marked 36, being supported like arches on the outer wall 24 of the shaft. Here, in the case of cement shaft kilns the dividing walls 25, 26, 27 are provided only in the region of the sintering zone although they may possibly extend still further upwards and downwards into the neighbouring zones.

The kiln shaft configuration according to the invention can be restricted to the said shafts sintering zone and parts of the directly adjacent zones not only when the shaft is divided by radially arranged dividing walls. On the contrary, all the measures according to. the invention described in conjunction with Figs. 2 to 4 for shaping the kiln shaft can be applied analogously to only the upper.

part of the said shaft in order to achieve the desired effect.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. A furnace for burning materials such as cement, lime, dolomite and the like, comprising a hollow kiln shaft having an inner wall, a portion of which encompasses and defines a sintering section, a centrally arranged core member disposed within said hollow kiln shaft and extending at least into said sintering section, said core member having its peripheral wall surface substantially equidistantly spaced from said inner wall of said shaft to define a chamber into which said material to be burnt is directed, cooling means extending through and beyond said core and defining duct means through which a cooling medium is directed for controlled cooling of said core, and means in communication with said cooling means for regulating the rate of flow of said cooling medium through said duct means to ensure that in any horizontal cross-section of said furnace including said cham her a substantially uniform temperature is obtained to effectuate substantially even burning of said material when disposed Within said chamber.

'2. A furnace according to claim 1, said inner wall of said shaft being shaped to define a geometric configuration having two different radii of curvature.

3. A furnace according to claim 1, said core including a fireproof covering partly surrounding said duct means.

4. A furnace according to claim 1, some portions of said duct means being disposed closer to each other within one part of said core and other portions of said duct means being spaced from each other to a greater extent in another part of said core, whereby the temperature conditions within said kiln shaft may be varied.

5. A furnace according to claim 1, wherein said chamber between the shaft wall and the wall of said core is oval-shaped.

6. A furnace according to claim 1, said core being hollow and defining duct means therein, through which a stream of coolant is directed in such a manner that said coolant passes through said duct means in opposed directions.

7. A shaft kiln for burning cement, lime, dolomite and similar substance, whereby the shaft of said kiln encloses a centrally arranged core extending from the top end of said shaft through a first zone in which sintering takes place toward a second zone located adjacent the lower end of said shaft; comprising cooling means extending from said top end lengthwise of said shaft and within the interior of said core toward said second zone, said cooling means including adjacent duct means for circulating a coolant from the upper end of said core through the interior thereof along said sintering zone back toward said upper end of said core, whereby thermal conditions of the effective space of said shaft, which is bounded by an inner wall defining said shaft and an outer wall defining said core may be regulated, and means connected with said core on which said duct means are accommodated, said shaft being subdivided into a plurality of separate cross sectional areas by means of dividing walls forming part of said core, said duct means being accommodated in said dividing walls.

8. A shaft kiln for burning cement, lime, dolomite and similar substance, whereby the shaft of said kiln encloses a centrally arranged core extending from the top end of said shaft through a first zone in which sintering takes place, toward a second zone located adjacent the lower end of said shaft; comprising cooling means extending from said top end lengthwise of said shaft and within the interior of said core toward said second zone, said cooling means including adjacent duct means for circulating a coolant from the upper end of said core through the interior thereof along said sintering zone back toward said upper end of said core, whereby thermal conditions of the effective space of said shaft, which is bounded by an inner wall defining said shaft and an outer wall defining said core may be regulated, and means connected with said core on which said duct means are accommodated, said effective shaft space being subdivided into cross-sectional areas of approximately equal size by means of dividing walls, each of said dividing walls forming an angle of to an adjacent dividing wall.

9. A shaft kiln for burning cement, lime, dolomite and similar substance, whereby the shaft of said kiln encloses a centrally arranged core extending from the top end of said shaft through a first zone in which sintering takes place toward a second zone located adjacent the lower end of said shaft; comprising cooling means extending from said top end lengthwise of said shaft and within the interior of said core toward said second zone, said cooling means including adjacent duct means for circulating a coolant from the upper end of said core through the interior thereof along said sintering zone back toward said upper end of said core, whereby thermal conditions of the effective space of said shaft, which is bounded by an inner wall defining said shaft and an outer wall defining said core may be regulated, and means connected with said core on which said duct means are accommodated, said core being constituted by dividing walls, each of said dividing walls being of substantially equal dimensions and being provided with the respective duct means for directing a stream of coolant therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 303,456 Roe Aug. 12, 1884 1,989,072 Billinghurst Ian, 29, 1935 2,278,189 Barnes Mar. 31, 1942 2,464,304 Gottlieb d. Mar. 15, 1949 FOREIGN PATENTS 828,944 France June 3, 1938 

